Furnace



Aug 1.7, 1937. H. o. HALDEN 2,090,328

FURNACE Filed Aug. 8, 1935 Patented Aug. 17, 1937 UNITED STATES PATENT OFFICE FURNACE Application August 8, 1935, Serial No. 35,337

Z Claims.

This invention relates to furnaces, and more particularly to the construction and operation of plants having two separate furnaces adapted to burn two different fuels.

In many establishments there is available a limited quantity of waste material, such as wood refuse, which has an appreciable heating value. 'I'his material must be burned and the heat therefrom utilized. At the same time it may be necessary to burn another fuel, such as coal, for the generation of steam. While it is possible in some cases to burn both fuels in a single furnace, it is often difficult to design a furnace which will operate satisfactory and eiiiciently under such conditions. On the other hand, if two furnaces are utilized, it is undesirable for many reasons and particularly from the economic viewpoint to provide a separate steam boiler and a separate stack for each. A difficult problem is therefore presented as to how the heat from the fuel can best be recovered and the necessary draft for both furnaces obtained. Further problems are presented in avoiding heat losses caused by eX- cess air in the refuse-burning furnace, and in so g5 constructing this furnace as to facilitate the introduction of fuel.

It is accordingly one object of the invention to provi-de a simple and eiiicient apparatus for burning two different fuels and recovering the heat therefrom.

It is a further object of the invention to combine a refuse-burning furnace with a steamgenerating furnace fired with a different fuel, and to obtain efficient combustion of both fuels,

adequate recovery of heat, and a long life for the apparatus required.

It is a further object of the invention to combine a refuse-burning furnace with a steamgenerating furnace fired with a different fuel, to

make possible the introduction of the refuse into its furnace in a simple manner, and to maintain a high over-all eiciency.

vWith these and other objects in view, as will be appar-ent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

Referring to the drawing illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

Fig. 1 is a somewhat diagrammatic view showing a refuse-burning furnace in section and an I associated steam-generating furnace in elevation;

and

Fig. 2 is a fragmentary View of a modification.

(o1. 11o-2s) 'Ihe embodiment illustrated in Fig. 1 comprises a steam-generating furnace III of suitable construction having a steam boiler II associated therewith. The boiler II is of a well-known water tube type having transverse drums, in- 5 cluding a lower rear water drum I2 and an upperk front water drum I4. It will be understood that the drums are connected by tubes (not shown) which form the boiler heating surfaces.

The furnace I0 is red with any suitable fuel, 10 and for this purpose I have shown a pulverizer I5 provided with the usual regulatable feeding mechanism I6 and arranged to supply pulverized coal and primary air through a pipe I'I to a burner vI8 mounted on the furnace wall. The 15 secondary air necessary for complete combustion of the fuel is supplied by means of a forceddraft fan 20 connected to the burner I3 by a duct 2 I. This duct may be provided with dampers 22 to control the rate of air flow. The furnace I is provided with the usual outlet duct 24 for the escape of the gaseous products of combustion after they travel past the boiler heating surfaces. This duct 24 may lead to a stack (not shown), and a damper 25 may be provided in the duct to control the rate of gas flow.

A separate furnace or incinerator 2'I is provided for the burning of waste material, such as wood refuse, and this incinerator is preferably open at the top to facilitate the introduction of the fuel. This construction is made possible by utilizing a down-draft grate of the water cooled type, and for this purpose I preferably utilize a row of horizontally spaced water tubes 28 which extend across the furnace between a lower header 35 29 and an upper header 30. The lower header is connected to the boiler drum I2 by means of a pipe 32, and the upper header is connected to the boiler drum I4 by means of a pipe 33. The grate y is thus connected into the circulation of the boiler I I. The iiow of water through the grate may be accelerated by providing the tubes 28 with steeply sloping portions 34 located Within the furnace and exposed to contact with the burning fuel. A door 35 is preferably located in the furnace wall 45 just above the tubes 28.

A second grate 3'I extends across the furnace beneath the tubes 28 to catch fuel which may drop through between the tubes. The grate 31 may be of the ordinary up-draft type, and a door 50 38 is preferably provided'in the furnace wall just above this grate. The space 39 below the grate 3'I is utilized as an ash pit, and a door 40 is provided in the furnace wall to facilitate removal of 55 the ashes, and to supply air for combustion of the fuel on the grate 31.

In order to provide sufficient draft to burn the refuse in the incinerator 21 and withdraw the gaseous products of combustion therefrom, I provide a duct 42 which connects the combustion space 43 between the grates 28 and 31 with the inlet of the fan 20. This duct is provided with an inlet 44 through which comparatively cool air may be admitted to mix with the gases before they enter the fan. In this way the fan is protected from high temperature gases which might cause damage thereto, and sufficient air is provided to support the combustion of the pulverized coal.

I preferably control the ratio between the quantity of gaseous products withdrawn from the furnace 21 and the quantity of air mixed with these products. By varying this ratio, it is possible to control the temperature of the mixture and prevent it from exceeding a predetermined maximum. In the preferred construction illustrated, a damper 46 is mounted in the air inlet 44, and this damper is actuated by means of an automatic regulator 41 connected to the damper by a rod 48. The regulator 41 is controlled by a temperatureresponsive device D mounted in the duct 2I and connected tothe regulator by a tube 5I The regulator 41 and control device 5B may be of any suitable construction, apparatus of this type being well-known and in common use in many arts. It will be apparent that the temperature of the gaseous mixture could be controlled by other means, such as a damper located at the outlet from the combustion chamber 43. However, such a damper would be exposed to very high temperatures, Whereas the damper 46 is located in a stream of comparatively cool air.

The operation of the invention will now be apparent from the above disclosure. Coal is delivered to the pulverizer I5 at a controlled rate by v the feeder I 6, and the pulverized coal and primary air pass through the pipe I1 to the burner i8. Secondary air is supplied through the duct 2l by the fan 20, and the coal burns in suspension in the furnace IG, the .gaseous products of combustion fiowing past the heating surfaces of the boiler I I and generating steam. The gases escape through the outlet duct 24, and the damper 25 is preferably controlled either manually or automatically to maintain a pressure in the furnace IB slightly below atmospheric pressure, thus protecting the furnace Walls from overheating without allowing excessive air infiltration. The supply of coal and air is varied in accordance with the demand for, steam, the variation in coal supply being effected by adjustment of the feeder IG, and the variation in air supply being effected by adjustment of the dampers 22 or by changing the speed of the fan 20.

`W aste materiaL'such as wood-refuse, is deposlted in the incinerator 21 through the open top thereof and is supported on the water tubes 28. Such particles as fall through between the water tubes will be supported by the lower grate 31. The deposit of the refuse maybe made whenever convenient, and need bear no definite relationship to the demand for steam from the boiler I I. The fan 2B will maintain a sub-atmospheric pressure in the combustion space 43, drawing air downwardly between the water tubes 28 and upwardly through the grate 31 to support combustion of the refuse. Ash will fall through the grate 31 into the ash pit 39 and can be removed through the door 4B. The fire can be poked or otherwisemanipulated if necessary through the comparatively cool air to enter through the inlet 44 and mix with the gases, thus reducing their temperature to a value considered safe, say 600 degrees Fahrenheit, while at the same time preheating the air forcoinbustion of fuel in thev steam boiler furnace I0. The regulator 41 will maintain this temperature substantially constant by adjusting the damper 46 automatically to admit more or less air whenever the temperature tends to rise or fall.

The combustion rates in the incinerator 21 and furnace I0 will be maintained in a substantially constant ratio, and the mixture flowing in the duct 2l will contain a substantially constant percentage of air, so long as sufficient refuse is supplied to the incinerator 21 to prevent the temperature of the mixture from dropping below the value for which the regulator 41 is adjusted. If excess air is present in the combustion chamber 43, it will lower the temperature of the gases escaping therefrom, and the regulator will partially close the damper 46, thus maintaining the temperature of the mixture and the proportion of air therein substantially constant. The heat liberated by combustion of the refuse will be utilized for generation of steam in the boiler I I. In case no refuse is being burned, the fan 2D will handle air only, and it will be necessary to reduce the air flow in proportion to the coal feed to maintain the desired fuel-air ratio for the furnace I0. Under these conditions the fan 20 may draw its air supply through the incinerator 21, or the damper 46 may be disconnected from the regulator 41 and placed in a Wide open position to admit air through the inlet 44.

In the modification illustrated in Fig. 2, means is provided to admit air through the inlet 44 if required for the combustion of the pulverized fuel, irrespective of the position of the automatic regulator 41. For this purpose, the damper 46 is replaced by an unbalanced damper 60 which tends to open upon a decrease in pressure in the duct 42. This damper is Aprovided with an arm 6I to which a weight 62 is adjustably secured. lThe arm 6I is connected to the regulator 41 by means of a flexible cable 64. The weight 62 and associated parts normally maintain the cable 64 taut, but if the air requirements are such as to cause an excessive suction in the duct 42, the damper will open to admit more air, and the cable will slacken.

It will be apparent from the above description that I have provided apparatus for burning two fuels which represent a considerable advance in the art. Ample draft is available for both the incinerator and the steam boiler furnace, and the apparatus is comparatively simple and inexpensive. rIhe fan is automatically protected from over-heating. The waste material can beeasily and conveniently deposited in the incinerator, and the heat from this fuel will be efficiently recovered. 4If excess air enters the incinerator, it will not 'affect the over-al1 efficiency of the installation, since such air will be utilized to support combustion of the coal,

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Fuel burning apparatus comprising a. furnace, means to supply fuel to the furnace for combustion therein, a steam boiler associated With the furnace, a rotary fan arranged to supply air at a pressure above atmospheric to the furnace to support the combustion of the fuel, means to supply air to the fan, an incinerator, a grate in the incinerator to support fuel thereon, and means to conduct the gaseous products of combustion directly from the incinerator and mix them with the air supplied to the fan without the interi vention of heat absorption apparatus between the grate and the fan, thereby reducing the temperature of said gaseous products of combustion and preheating the air before they enter the fan.

2. Fuel burning apparatus comprising a furnace, means to supply fuel to the furnace for combustion therein, a steam boiler associated with the furnace, a rotary fan arranged to supply air at a pressure above atmospheric to the furnace to support the combustion of the fuel, means to supply air to the fan, an incinerator, a grate in the incinerator to support fuel thereon, means to conduct the gaseous products of combustion directly from the incinerator and mix them With the air supplied to the fan without the intervention of heat absorption apparatus between the grate and the fan, thereby reducing the temperature of said gaseous products of combustion and preheating the air before they enter the fan, and means to control the ratio between the volume of said gaseous products of combustion and the volurne of the air supplied to the fan in accordance with the temperature of the mixture.

` HERBERT O'. HALDEN. 

